Patent GB-1082341-A (GB)
Title: Improvements in and relating to safety devices for aircraft take-off
Inventor: GROVER JOHN HERBERT HARDY
IPC: G05D1/00
Filed: 1963-05-13
Abstract: 1,082,341. Aircraft instruments. PHOENIX FLIGHT SERVICES (DEVELOPMENT) Ltd. Aug. 12, 1964 [May 13, 1963], No. 3725/63. Heading B7W. [Also in Division G1] In a device, Fig. 1, for monitoring aircraft take-off, a normally closed relay 3, 4 in an alarm circuit opens if and when the air-speed of the craft on the runway attains a pre-determined minimum take-off value, and a normally open relay 67 closes when the distance run by the craft reaches a predetermined value; if the minimum air-speed has not been reached by the time the predetermined distance has been covered, a warning device 1 is operated. Measuring air-speed.-In Fig. 4 (not shown), the static and dynamic pressures from a Pitot head are passed respectively to a casing (21) and to a flexible capsule (20) therein, movement of the capsule due to the difference in pressure being transmitted to the wiper (5<SP>1</SP>) of a rheostat (5); the value of air-speed at which the coil (4) of the normally closed relay is energized is set by adjustment of the rheostat (5) by a gear (23). In an alternative arrangement, Fig. 8 (not shown), the two pressures are applied via tubes (38, 39) on either side of a diaphragm (37) which, at the predetermined air-speed, is deflected sufficiently to operate a miroswitch (40); the said air-speed is determined by adjustment of a screw (42) via gearing (43, 44) actuated through a flexible drive by a crank (45), and is displayed (at 46). Fig. 11 (not shown) depicts an embodiment in which a pivoted arm (50) is deflected by the air-stream against the counter-force of an adjustable spring (52), to effect closure of a microswitch (40) at the predetermined air-speed. Measuring distance run.-In Fig. 3 (not shown), a toothed wheel (10) retractably lowered from the aircraft, contacts and is driven by the ground during the take-off run. The toothed wheel (10) drives a rotor arm (12) which, once per rev., engages a contact (13) to transmit a pulse to a coil (15), thus actuating, via a pivoted stirrup (16), an escapement mechanism (17) to advance the wiper (8<SP>1</SP>) of a rheostat (8). The distance at which a relay coil (7) closes its normally open contacts (6) is set by adjusting a rheostat (19) shunted across the coil (7). In a modification, Fig. 10, a ground-driven wheel 24 rotates a cam 31 through a worm 27, gear 28 and flexible drive 29. Every half-rev. cam 31 closes a set of contacts 32 to supply a pulse to a winding 33 of a step motor which drives, through gearing 35, a counter 36. Indicating apparatus.-Counter 36, which may be a modified commercial counter, has three registers, one set to the critical distance, the others to intermediate distances, and each arranged, when the register reaches zero to operate a microswitch 6, 6a, 6b. An airspeed measuring device, set at the critical airspeed, controls microswitch 40 which co-operates with microswitch 6 to operate either the alarm 1, which may be audible and/or visual, or a " safeto-take-off " lamp 49. Devices 102, 103, set at sub-critical airpseeds, control microswitches 40a, 40b which co-operate with microswitches 6a, 6b and relays 100, 101, respectively, to illuminate " adverse condition " lamps 104, 106, or " satisfactory condition " lamps 105, 107, at intermediate distances. Lamps 49, 104-107 may be located in the casing of the counter 36 (Fig. 9, not shown), and duplicate indications may be furnished by lamps paralleled across lamps 49, 104-107 and disposed around the aircraft's airspeed indicator (Figs. 12, 13, not shown).